1. Field of the Invention
The present invention is related to a single stage DC to DC electric power conversion circuit having a transfer gain variable by pulse-width modulation over a continuum from zero to beyond unity.
2. Description of Related Art
By definition, transfer gain of a power conversion circuit is the ratio of output voltage to input voltage. In order to provide output voltage regulation against dynamic variations in input voltage, the transfer gain must be variable. The transfer gain must also be variable in both directions (i.e., increase or decrease) to cope with input voltage variations in both directions. Taken into account the input voltage variations under abnormal conditions, like mains line brown-out or transient on lightning, the input voltage may vary over a very wide range.
Therefore, under a normal input voltage, the transfer gain must stay afar from their variable extremes to allow for such dynamics.
Conventional Buck or Boost converter designs have their optimal efficiency at one extreme of their transfer gain variable range. For the Buck converter, efficiency is best at unity transfer gain, which is the maximum possible value of the Buck topology. For the Boost converter, efficiency is best (also) at unity transfer gain, which is the minimum possible value of the Boost topology. But due to the aforesaid dynamic concerns, the transfer gain cannot be set to the extreme and the efficiency is therefore far from optimal under the normal operating conditions.
There exists a Flyback converter design, which can have optimal efficiency at the middle of its transfer gain variable range. Therefore a Flyback converter can be designed with optimal efficiency under normal operating conditions. But the optimal conversion efficiency of Flyback topology is not as good as those of the Buck or Boost topologies. This is because all of the power transferred to the output must undergo a lossy electro-magnetic conversion process in a Flyback converter.
Conversely, in Buck or Boost converters, a large part of power is directly fed through to the output without undergone the same lossy process; this is particularly true at their optimal efficiency point where transfer gain is near unity. For this reason, Flyback converter is no better than Buck or Boost converters in terms of efficiency.